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Recalled centre Jamie Roberts feared an early bad injury had ended his tour, but three weeks on he will be battling on Saturday to earn the Lions their first series win in 16 years.

After a strong running performance in the 47-17 win over New South Wales on June 15, Roberts seemed destined to face the Wallabies over the next three weekends in the 125th anniversary Test series.

But four minutes from the end he damaged his hamstring and his Test dreams were shattered. It was a moment the newly qualified doctor had dreaded.

"As soon as I was walking off the pitch in the Waratahs game I thought I was going home. I have to say a massive thanks to the medical team who worked wonders with the rehab," Roberts said on Wednesday.

"I had a scan the day after the injury and then they sat me down and said they would keep me on tour, stay positive and do everything in their power to get me fit....The gods have smiled on me."

Roberts said he did not run until Friday last week and did not feel 100 percent fit.

"Obviously, they decided not to put me in contention for selection last week, but I'm delighted to make it this week," he said.

"Seeing the boys lose by a point last week was heartbreaking, really, but the series is poised nicely (at 1-1) and we've got a golden opportunity on Saturday."

Roberts forced his way into the Lions Test side in South Africa four years ago and figured in the first and second defeats to the Springboks before injury ruled him out of the third game.

After a great performance for Wales in their Six Nations championship victory over England he looked a certainty to start in this series.

The question was, would it be with his 2009 midfield partner Brian O'Driscoll or his Welsh colleague Jonathan Davies. The selectors decided on Wednesday to drop the great Irishman O'Driscoll and go with an all-Welsh midfield.

"I see it as a responsibility, I don't see it as pressure. I've been picked to do a job and it is important I deliver. I've always thought that I thrive under pressure in big games -- it's where I like to play," said the 26-year-old.

"The higher the pressure, the more responsibility is put on me, the more I thrive and the more I enjoy it. There is no bigger stage to play on. It's a Lions deciding Test match, it's all or nothing, and this is the time you have to deliver.

"Brian is one of the most incredible players I have played with or against in rugby union. I am sure he will be remembered as a Lions legend.

"Brian is a leader and I've tasted that playing alongside him. He's a force, and it is up to me and Jon now to lead the way in midfield and take that responsibility and thrive under the pressure.

"The coach picks the team. Warren has picked the team he thinks will go out there and beat Australia on Saturday. That changes week in, week out, with injuries and performances."

Roberts and Davies had been expected to get the nod to pair up throughout the series, especially with England's blockbusting Manu Tuilagi struggling with a shoulder injury, but Roberts' injury wrecked those plans.

Davies had a superb first Test in Brisbane alongside O'Driscoll and defended well in Melbourne. Now he and Roberts have to find gaps in the Aussie defence to steer the Lions to a series win.

"Over the last three years with Jon we have become the most capped centre partnership Welsh rugby has seen. We've got experience and we've played together a lot," said Roberts.